$A$ hypothetical electromagnetic wave is shown in the figure. Find out the wavelength of the radiation.

(N/A) The wavelength $(\lambda)$ is the distance between two successive peaks or two successive troughs of a wave.
In the given figure, the distance between a peak and the next equilibrium point is $2.16 \text{ pm}$.
Since a full wavelength corresponds to $4$ such segments (peak to equilibrium, equilibrium to trough, trough to equilibrium, equilibrium to peak), the wavelength is:
$\lambda = 4 \times 2.16 \text{ pm} = 8.64 \text{ pm}$